May's Weather, Model Data and Analogues Suggest a Mixed Summer

Many times I've noticed through the years how Mother Nature will tip her hat as to the weather likely for the next season late in the current season and I feel with this May is one of those cases. That, along with computer generated outlooks and previous and newer El Nino analogues suggest this is the case for the summer.

In my last blog, I stated strongly contrasting air masses would rule the second half of May...cold...warm with more storms and rain as a result. The second half of May certainly lived up to that projection with several warm days rudely interrupted by notable cold snaps. Impressive cold snaps that actually brought temperatures down into the 30s along with scattered frosts as late as the 23rd. Take a look at these low temperatures for the morning of the 23rd across Southeast Lower Michigan.

However, in spite of the of the cold interjections, May still managed to average several degrees above normal and that was primarily a result of a very warm first half of the month. Temperatures the first couple of weeks averaged at one point as much as 10 degrees above normal before settling back to about half of that. Analogue projections had called for a changeable spring with colder than average weather early, moderating to normal and above normal by the time May rolled around along with overall, drier than average predominate conditions. March's temperatures averaged below normal across the region along with drier than normal conditions, where as warmer winds commenced in April bringing temperature averages up a couple degrees above normal weather but with continued drier than average rainfall. By the end of April, most areas were two inches or more below normal for rainfall.

May's weather was a mixed bag as far weather with again warm and cool air masses interchanging but with a decided preference to warmer. Not surprising, along with the conflicting air masses was the pick up in wet weather. After two months of relatively dry weather; May's rainfall averaged near normal to above normal (especially at the end of the month and over the south) with rather frequent periods of showers and strong thunderstorms. Actually the month's rainfall was generally below normal across much of Southeast Lower Michigan until the last two days when very heavy rains from a stalled front and attending low pressure wiped out most deficits for the month. Interestingly, while the heavier rains wiped out the deficit for May and led to a normal to above normal rainfall statistic across the south (Ann Arbor through metro Detroit) for May and the spring; areas to the north remained below normal for the spring. This is one of those cases across the south where the trend of the spring was actually dry, yet the rainfall amounts were normal to above but mainly due to just two days, the 30th and 31st of May.

Note the heavy rainfall map across Southeast Lower Michigan From 8am 5/30/15 - 8am
5/31/15 and this does not include the rainfall after 8am on Sunday, the 31st. 

 


This is a summary of the past - now what about the future?

Summer 2015 Outlook for Southeast Lower Michigan

Temperatures :

Overall; I look for temperatures to average around normal but with notable swings as the upper low and troughing in eastern Canada via for dominance against upper ridging, aided and at times, even suppressed by El Nino affected winds across the south. This is a difficult forecast as we dealing with two distinctive upper wind patterns, not always present in such fashion in the summer. The outcome is not only going to be affected by conflicting air masses but also with the timing and the extent of dominance by each air mass. 

That being said; In the end, I look for  temperatures averaging between +1.5 degrees and -1.5 degrees of the summer norms across Southeast Lower Michigan...a bit wider range than typical. Interestingly, this oscillating range may very well sum up the summer on a week or two and/or a monthly basis. 

 

Rainfall:

I look for rainfall to be quite variable as mixed data presents conflicting results and where and how much may also be exasperated more than what is typical for many summers. Taking all data (past and present) into account; rainfall is expected to be above normal over the southern sections of Southeast Lower Michigan and normal to possible even below across the Saginaw Valley and Thumb Region. As with temperatures, timing of the wettest and driest periods will be quite variable - not unlike the spring.

 

Look for my entire, detailed Outlook coming this week.

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian

 

Change in Upper Air Pattern Mid-May Liable to Bring More Contrasting Temperatures and...

I my blog regarding May's weather outlook I stated; I expected a warmer than normal May and thus far, Southeast Lower Michigan is averaging 8 - 10 degrees above normal thru the 13th. In addition, on 5/2 when I wrote the blog I stated:

"Why there is still the risk of a frost or freeze, none looks likely in the next week to 10 days anyway and there's less than a 30% chance through the month with the above normal temperatures. I'll keep the blog updated if the risk does arise if colder air masses make their way out of Canada".

I stated that because even though I expected a warm May overall, sharply contrasting air masses have been the rule this spring and I expected May to be no exception. After days in the 80s (including record territory), sharply colder air from Canada has aggressively plowed back across the region, driving temperatures down some 30-35 degrees recently! While temperature swings of 30-40 degrees in the month of May happen, it's not as commonplace as its spring month counterparts of March and April across Southeast Lower Michigan.

Our upper air pattern has reverted back to "ridge-trough pattern" of April as opposed to primarily ridge the first two weeks of May. The projected pattern discussed on the 2nd served well the first two weeks of the month (or as stated  "next week to 10 days") with above to much above temperatures. In addition, I stated I would update if the need arises after that period and the need has come....

Remainder of May Outlook
After a cold start and risk of scattered frost across the region overnight into Thursday morning as a rather strong high pressure dominates, look for temperatures to start a moderate climb once again through the 60s and into the 70s and breaking into the 80s over the weekend. In addition, the risk of showers and thunderstorms will be on the increase as the warmer air rudely surges back into the region. With this contrasting pattern in the works the next few week, severe weather potential also rises.

Looking ahead, I expected this oscillating pattern to be more the rule than the exception through  much of the remainder of the month. While temperatures will average above normal for the month, enough cold air will also be able to make it down occasionally to bring the possibility of a frost and/or freeze.

The old adage of planting after Memorial Day (and it comes the earliest possible this year) still seems the best advice - especially in the more frost/freeze prone areas of Southeast Lower Michigan!

 

Making weather fun while we all learn, Bill Deedler -SEMI_WeatherHistorian

Analogues and Guidance Indicate a Warmer and Somewhat Drier May In Store for Southeast Lower Michigan

Thus far, the current spring pattern has evolved as indicated by both analogues and recent guidance. A colder than normal March evolved into a near normal to above in April as temperature patterns projected and in actuality; transitioned from below normal to above. The timing of the pattern change has been somewhat ahead of the timing of both spring analogues and models by about a week or two week. But, I'm not complaining after last winter and early spring with spring development, now in full force.

TEMPERATURES
Spring analogues for May called for a near normal May temperature-wise while latest guidance indicates above normal temperatures. With out timing of pattern changes seemingly ahead of past analogues, above normal temperatures are the best forecast. Typically May's average high temperatures start out in the mid 60s and warm to the mid 70s by the close. Overnight lows begin the month in the mid 40s and rise to the mid 50s by the close. Why there is still the risk of a frost or freeze, none looks likely in the next week to 10 days anyway and there's less than a 30% chance through the month with the above normal temperatures. I'll keep the blog updated if the risk does arise if colder air masses make their way out of Canada.

RAINFALL
Drier than normal or average spring conditions were projected by both the analogues and models, and continue to be upheld by latest precipitation guidance for May. Local analogues projected Spring rainfall would average at least an inch or two below normal across all of Southeast Lower Michigan. Thus far this spring through the end of April, precipitation has averaged around two inches below normal. Latest model projections continue the drier than average pattern with below normal rainfall. Note the CFSv2 is calling for a notable bull-eye of below normal rainfall to our south, over the Ohio Valley. Interesting since this is the area that has been most active with precipitation the past several seasons on average. May is generally one of our wetter months with around three inches of rain usually falling - therefore this dry pattern established bares watching for the growing season.

Making weather fun while we all learn, Bill Deedler -SEMI_WeatherHistorian